In recent years, demand has been increasing for mobile services based on IP architecture. Frameworks that efficiently register positions for service use of a mobile user are being sought in mobile networks. Particularly, when using a plurality of types of services and each of the services belongs to a different domain, a terminal has to simultaneously execute a plurality of position registrations corresponding to a plurality of types of services with respect to a home agent, and therefore, a framework that efficiently carries out this position registration is preferable.
Several service providers that provide end users with so-called multi-home environments in which the services belong to different domains already exist. These end users are able to simultaneously connect to this plurality of types of service providers by the assignment of a plurality of IP addresses to their terminals.
Such a state of simultaneous connection is already possible with IPv4 and IPv6. However, the connection method is limited to a fixed connection.
In this regard, in recent years, the demand for mobile services has grown and such multi-home environments have become desirable in mobile terminals as well. As mobile services, there currently are IP telephone services, Internet connection services, email services, Voice Over IP (VoIP) services, etc., but when using for example the above IP telephone services and Internet connection services, it is desirable for the end user to connect the two service providers providing these two services simultaneously.
In this case, the IP address assignment of a mobile terminal of an end user changes due to movement, so special mobile management technology is desirable to maintain the above simultaneous connection state. The present invention is proposed based on the related technical background. This background art will be specifically explained below.
[IPv6 Multi-home Environment]
In IPv6, a broad address space is assigned to the end users. This enables each end user to possess a plurality of global IP addresses.
There are three types of IPv6 addresses: unicast, multicast, and anycast. Among these, unicast is further broken down into the three following types depending on the valid scope of the address. Note that the above global IP address to be assigned to the end user is the global unicast address a) below.                a) Global unicast address: A globally valid unicast address with no limitation of scope.        b) Site local unicast address: A unicast address defined as being valid only within the same site, but now discarded.        c) Link local unicast address: A unicast address valid only within the same link (subnet) and used for address resolution with a different host on the same link and for communicating control information such as routing protocol.        
FIG. 8 is a view illustrating the format of the above a) global unicast address. In this figure, the global unicast address is broadly divided into a prefix and an interface ID which is automatically created by the operating system inside the terminal on the basis of a Layer 2 MAC (Media Access Control) address.
This prefix, as illustrated, is broken up into a 48 bit prefix comprised of a 3 bit header and a 45 bit global routing prefix and of a 16 bit subnet ID. The former 48 bit prefix is the portion that is automatically assigned by the service provider when the end user registers for a service provider.
On the other hand, the end user can use any subnet ID, where 216 number of independent subnets can be freely defined. Accordingly, in the above mentioned multi-home environment, an end user is able to selectively use the different registered services within a single environment by the subnet IDs. This can be illustrated as follows.
FIG. 9 is a view schematically illustrating an example of the above multi-home environment. In this drawing, the user network of the end user comprises, for example, a computer or other apparatus PC, a TV or other apparatus TV, and a mobile device or other mobile node MN. These use the access network of a telephone carrier to connect to three providers A, B, and C and receive corresponding services.
In this case, the providers A, B, and C have unique prefixes different from each other. The above apparatuses PC, TV, and MN also have unique prefixes different from each other. Between these providers and apparatuses, independent tunnels A, B, and C are formed through a center broadband router. Due to this, the above providers and apparatuses, if not corresponding to each other, cannot access each other.
Note that, the above-mentioned broadband router has an IPv6 pass-through function. The IPv6 apparatus is able to directly communicate with the outside.
With the global unicast address illustrated in FIG. 8, an end user can have 216 number of subnet IDs, so an end user can contract with a plurality of (for example, three) service providers (A, B, and C) and the service providers can assign their IP addresses (global routing prefixes) to the end user. Thus, an end user can simultaneously connect to a plurality of types of service providers.
Note that the same is also possible for IPv4, but there are major differences (merits) in IPv6 from IPv4 in the following points.
1) The assigned address space is broad.
2) When a broadband router is used, the address of each apparatus (PC, TV, and MN) of the end user becomes a private address under the IPv4. However, under the IPv6, each apparatus itself has a global address, so it becomes possible to use external services which require direct communication.
Above, an IPv6 multi-home environment for a user network was explained. Next, a mobile IP will be explained. The mobile IP is a base technology in explaining the IPv6 multi-home environment covering a mobile network.
[Mobile IP]
FIG. 10 is a view explaining in brief a mobile IP forming the basis of the above mobile network. In this figure, Mobile Node (MN) indicates a terminal (mobile terminal), AR an advertising router, HA a home agent, CN (Correspondent Node) a terminal of the other party in the communication, and AAA (Authentication, Authorization, and Accounting) an authentication/authorization server.
Further, the arrows in the figure (e, f, g, etc.) represent the operations occurring between the corresponding devices, wherein                e: represents an access authentication taking place between AAA and MN when the terminal MN first connects to the network NW,        f: represents a mobile IP authorization taking place between HA and AAA,        g,g′: represent prefix advertisements, that is, Router Advertisements,        h,h′: represent position registrations from MN to HA, that is, Binding Updates, and        i,i′: represent transmission/receipt of data packets between CN and MN.        
When engaging in IP communication in a radio network, if the terminal MN moves, the network that the MN connects to changes and accordingly the IP address assigned to the terminal MN changes at its new location. At this new location, when sending a signal from the terminal MN to another party, communication is possible by using the IP address of the MN. Conversely, when trying to send a signal from the other party of communication, for example, CN, to the terminal MN, it is desirable to know in advance the fixed destination and the destination address of the other party of communication.
The “fixed destination” refers to a device inside a network domain called a home network which is accessible from other networks. In this network domain, a permanent address is assigned to a terminal MN. Further, each time the terminal MN moves, a position registration request is sent to this home network so as to link the address assigned at the new location to the permanent address. Due to this, packets from the CN are transferred to the MN through the home network, thus allowing arrival of packets at the MN.
Such technology is called “mobility management”. Various systems have been proposed. A leading technology among these is the mobile IP illustrated in FIG. 10. In this mobile IP, an address assigned to an MN terminal in the network of the new location is called a care-of address (CoA) (CoAa or CoAb in the figure). On the other hand, an apparatus called a home agent (HA) is installed in the home network. The HA manages the permanent home address HoA assigned to the terminal MN while binding with the care-of address CoA. Then the HA broadcasts a router advertisement (RA) relating to the HoA to the surrounding routers. Due to this, all packets sent addressed to the HoA are forwarded to the HA, then the packets are transferred to the network to which the terminal MN is being connected.
Thus, to enable packet transfer to the MN through the HA, it is desirable for the terminal MN to register its position. To do this, the MN at the new location sends a binding update message to the HA. The position-registered terminal MN forms a tunnel to the HA by IP in IP or IPSec or the like so as to send and receive packets through this tunnel.
Note that, as known art according to the present invention, there are the following Patent Literature 1, Patent Literature 2 and, Patent Literature 3.
Patent Document 1 describes a first home agent apparatus registering as a care-of address a second home address used in a domain network of a new location when a mobile terminal moves to another domain network different in service form.
Patent Document 2 describes, when packets destined for a representative home address or subsidiary home address arrive from any communication node, searching through the held registered information for binding information including the address and transferring packets to the corresponding care-of address.
Further, Patent Document 3 describes a mobile node moving between subnets of different domains by using a virtual network prefix-based IPv6 address as a care-of address for a home agent which manages the mobile node.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-129210
Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-101715
Patent Document 3: Japanese Laid-Open Patent Publication No. 2002-261806
FIG. 11 is a view for explaining the problems when applying a multi-home environment to a terminal (mobile terminal). The differences from the FIG. 9 are that the user network of FIG. 9 is replaced with a radio network and that the mobile terminal MN connects to a different radio network each time it moves. Further HA, AR, etc. illustrated in FIG. 10 are also described.
When using the mobile IP illustrated in FIG. 10, the IP address of the terminal MN to be recognized by the other party for the connection is the home address HoA. Accordingly, in the case of a multi-home environment, the connections are between the home agent HA and the service providers (A, B, and C), and therefore, it is desirable to link respective home address HoA (see HoAa, HoAb, and HoAc in FIG. 11) to each of the homes of the service providers (A, B, and C).
Further, it is desirable for the terminal MN to store a different care-of address CoA for each location for each of these HoAa, HoAb, and HoAc (refer to CoAa, CoAb, and CoAc; CoAa′, CoAb′, and CoAc′; CoAa″, CoAb″, and CoAc″ of FIG. 11). Therefore, it is desirable to register the positions of HoA and CoA for each of the providers A, B, and C.
Further supplementing the explanation of FIG. 11, a terminal MN moving to three locations corresponds to the terminal MN in the user network of FIG. 9 and, inside the terminal MN, there are three subnet IDs (FIG. 8) corresponding to the providers (A, B, and C).
Further, a CoA-HoA tunnel is formed between the terminal MN and home agent HA for each service provided by the providers (A, B, and C). Further, each time the terminal MN moves, the tunnel is reformed like CoA-HoA, CoA′-HoA, and CoA″-HoA. Accordingly, the home address HoA does not change regardless of the movement of the terminal MN, while the care-of address CoA is updated along with the movement. In this case, the home agent HA controls the connection between the terminal and the provider for each HoA.
As explained above, each time the terminal MN moves, a binding update message for position registration must be sent and received between the terminal MN and the home agent HA for exactly a number of times corresponding to the number of providers (A, B, and C), that is the number of HoA-CoA, HoA-CoA′, and HoA-CoA″. Further, the authentication and authorization required when registering positions also must be carried out for exactly a number of times corresponding to the number of providers (A, B, and C). Therefore, a packet loss and packet delay are liable to occur. Ultimately, this degrades the quality of transmission in the mobile communication system.